<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>

        html,body {
            margin: 0;
            height: 100%;
            background-color: #272823;
        }

        div {
            width: 250px;
            height: 350px;
            background-image: linear-gradient(#fff,#c7c4c4);
            margin: 200px auto;
            position: relative;
        }
        
        div::after {
            content: "";
            position: absolute;
            border-left: solid 80px #272823;
            border-bottom: solid 80px #eee;
            left: 0;
            top: 0;
            box-shadow: 7px 7px 7px rgba(0, 0, 0, 0.3);
        }


    </style>
</head>
<body>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <main>123</main>
    <main>456</main>
</body>
</html>